This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Specific Aims We hypothesize that LepRb neurons in the extended perifornical area (exPFA), specifically LepRb(Gal) neurons, play a crucial role in mediating anorexigenic leptin actions via PVN outputs and thus control feeding behavior. Our overall goal is to understand the physiologic function and underlying neuronal network of LepRb(Gal) neurons as well as to investigate the overall population of LepRb neurons in the exPFA. We will thus: 1. Determine the role of LepRb(Gal) neurons in physiologic leptin action. We will examine the phenotype of mice with targeted deletion of LepRb in galanin neurons (LepRbKO(Gal) mice) to determine the contribution of LepRb(Gal) neurons in leptin dependent regulation of energy homeostasis. We will specifically investigate any perturbation in body weight, food intake or energy expenditure in these mice with disrupted LepRb in Galanin neurons. Thus, we expect LepRbKO(Gal) mice to be hyperphagic and obese. 2. Investigate the regulation of LepRb(Gal) neurons. We will use reporter mice to visualize LepRb(Gal) neurons immunohistochemically and define regulatory mechanisms of LepRb(Gal) neurons. We will determine if LepRb or LepRb(Gal) neurons in the exPFA are stimulated by leptin or physiological stimuli like fasting and refeeding (via cFos induction and/or regulation of galanin) and if they co-express the inhibitory transmitter GABA. We will further study the contribution of ARC inputs (e.g. melanocortin system) to regulate LepRb(Gal) neurons by investigating LepRb(Gal) regulation after blockade or ablation of ARC inputs. 3. Investigate the neuroanatomic circuits of LepRb(Gal) neurons. We will define axonal projection sites of LepRb(Gal) neurons (e.g. the PVN) by using traditional and novel tracing methods (LepRb or galanin neuron-specific tracer expression in the exPFA). Furthermore, we will identify the neurons that are innervated by LepRb(Gal) neurons (e.g. in the PVN) or that innervate LepRb(Gal) neurons (e.g. from the ARC), by using LepRb or galanin neuron-specific expression of anterograde or retrograde transsynaptic tracers in the exPFA.